Tandem master cylinders are known comprising a primary hydraulic circuit and a secondary hydraulic circuit, each of the circuits having a primary and secondary piston respectively. The primary piston and the secondary piston are made to slide in a bore formed in a body of the master cylinder. The primary piston and the secondary piston define a primary chamber and a secondary chamber respectively. The primary chamber and the secondary chamber are filled with hydraulic fluid or brake liquid via a primary hydraulic fluid reservoir and a secondary hydraulic fluid reservoir respectively.
The master cylinder comprises a first, second, third and fourth sealing means. The first means is situated in the primary chamber and forms a primary sealing cup. This primary sealing cup is positioned at an inlet of the primary chamber. This primary cup isolates the primary chamber from the outside of the master cylinder. The second sealing means is situated in the primary chamber and forms a primary seal. This primary seal is positioned between a wall delimited by the bore of the master cylinder and the primary piston. This primary seal controls the passage of hydraulic fluid from the primary reservoir to the primary chamber according to the position of the primary piston in the bore of the master cylinder.
The third sealing means is situated in the secondary chamber and forms a secondary sealing cup. This secondary sealing cup is positioned at an inlet of the secondary chamber and isolates the secondary chamber from the primary chamber. The fourth sealing means is situated in the secondary chamber and forms a secondary seal. This secondary seal is positioned between a wall delimited by the bore of the master cylinder and the secondary piston. This secondary seal controls the passage of hydraulic fluid from the secondary reservoir to the secondary chamber according to the
The primary seal, the secondary seal, the primary cup and the secondary cup are each housed in a peripheral groove hollowed out in the wall of the master cylinder and surrounding the piston. These seals and cups are made of rubber and possess profiles with parts folded in the shape of a U. These seals and cups form rings with an axis of revolution coaxial to the axis of movement of the piston in the bore of the master cylinder.
At rest, that is so say when the brake pedal of the vehicle is not actuated, the primary chamber and secondary chamber are filled with brake liquid coming from the primary reservoir and the secondary reservoir respectively. During braking, that is to say when the brake pedal is actuated, the flow of brake liquid coming from the reservoirs into the primary chamber and into the secondary chamber is blocked. In point of fact, while advancing along the wall of the master cylinder, the primary piston and the secondary piston are positioned with respect to the primary seal and the secondary seal respectively so that the primary seal and the secondary seal block the passage of liquid from the primary reservoir and the secondary reservoir to the primary chamber and secondary chamber respectively. The pressure inside the primary chamber and the secondary chamber then increases. It follows that brake liquid is injected from the chambers into the braking devices of the vehicle.
During the movement of the primary piston along the wall of the master cylinder, for example, the primary piston is caused to rub against the primary seal. When sudden braking occurs, that is to say when the brake pedal is suddenly actuated, the primary seal may roll on itself inside the corresponding groove, or else extrude from the groove or even tear. Thus, there is the risk of arriving at a situation where the primary seal no longer acts as a seal for the primary chamber in relation to the primary reservoir. The fluid contained in the primary chamber may then creep between the wall and the primary piston. The result is braking which is made much less effective or may even become deficient. It will be understood that such braking may thus harm the safety of a driver of the vehicle.
In order to solve this problem, in the invention, the stiffness is increased of a wing of the seal concerned which bears against the piston. Accordingly, in the case of a sudden return of the latter or during transport, the risk of deterioration of the seal is reduced. In order to increase this the risk of deterioration of the seal is reduced. In order to increase this stiffness, it would be possible to increase the size of the primary or secondary seal so as to prevent the primary or secondary seal from rolling on itself or tearing.